<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>demo 2-31</title>
	</head>
	<body>
	</body>
	<script>
		function fn(name,age){
			name = name;
			age = age;
			console.log(name+","+age);
		}
		function fn2(name,age){
			name = (typeof name !='undefined'?name:'tom');
			name = (typeof age !='undefined'?age:17);
			console.log(name+","+age);
		}
		function fn3(name='tom',age=17){
			console.log(name+","+age);
		}
		fn();
		fn2();
		fn3();
	</script>
</html>